1. Field of Invention
The present invention relates to an solid state planar light source structure, and more particularly, to a bendable LED planar light source structure, a flexible structure and a manufacturing method thereof, which is directly bonded with a bendable metal sub-mount having a circuit, so as to enhance the thermal conduction effect, thereby achieving preferable photoelectric characteristics and higher light-emitting efficiency.
2. Description of Related Art
Solid state lighting (SSL) is a micro solid state light source having the advantages of desired shock resistance, power saving, long life-span, and diversified and pure colors, which meets various application demands and has gradually become a popular light source. SSLs are mainly classified into visible light SSLs and non-visible light SSLs, and the visible light SSL is mainly applied in back light, interior lighting, landscape lighting, mobile lighting, and the like. Currently, there are many difficulties when applying the feature of bendability to SSL, for example, first, SSL dies are made of rigid and friable materials and cannot be bent. Next, when the SSL is applied in the back light module, the SSL lamp is jointed with a substrate having a large area, such that heat dissipation is poor, and failure of the SSL element is accelerated. Further, the SSL substrate itself has the effect of light-absorbing, such that the forward light-emitting efficiency of the SSL is reduced.
Since the SSL chip is a non-directional light source, the forward emitted light of the SSL Chip is rather limited, and with the additional absorption effect of the substrate, the internal absorption loss of the SSL becomes excessively large, thus, the external light extraction efficiency is relatively low. Currently, some manufacturers are researching how to improve the light emitting efficiency and to prevent the substrate from absorbing light. Generally, a substrate transposing technique is used, or a layer of reflect surface is coated on the substrate, or large-scaled SSL dies, i.e., greater than or equal to 40 mils, are used to generate high power, and thereby increasing the forward emitted light. However, using the large-scaled (≧40 mil) SSL dies results in problems of poor current distribution and poor light-emitting efficiency due to the heat accumulation. In order to improve the heat dissipation efficiency of the SSL, the SSL chip generally uses a heat sink substrate or has a heat sink compound coated thereon to be packed into an SSL lamp. However, the heat dissipation effect is also limited. In addition, in order to adjust the light axial area, the current large-size SSL planar light sources (back light plates) are all formed by using SSL lamps together with light guides, or by using an array of SSL lamps, thus, the SSL planar light source is not bendable.
In U.S. Pat. No. 6,274,924 titled Surface mountable LED package and provided by the LumiLeds Corporation, a light emitting module capable of enhancing the SSL light emitting efficiency is disclosed. Referring to FIG. 1, the light emitting module 100 includes an embedded structure of a lamp shade 20 and a heat-absorbing socket 12, with a light emitting diode (LED) chip 16 being accommodated therein. The LED chip 16 is put into a module with a high reflective metal through flip chip, and the module also has a sub-mount 18 with high thermal conductivity. The packaged SSL module is relatively rigid and not bendable.
Moreover, referring to FIG. 2, Luxeon SSL back light module is manufactured by the current SSL back light module processing method of international manufactures, for example, Direct Type, and it can replace the current cold cathode fluorescent lamp (CCFL) back light module, without any light guides. SSL modules, e.g., 210, 220 and 230 shown in the figure, are arranged on a strip-shaped substrate in an order of green, red, blue, green . . . (GRBG . . . .), with the interval between each SSL module as 12 mm. The Luxeon SSL back light module provides a preferred amount of emitted light, however, since it includes SSL dies of more than 40 mils in size, the heat dissipation is poor, and the module is also not bendable. When the SSL is applied in a back light module, the SSL lamps are jointed with a large-sized substrate, such that the heat dissipation is poor, and failure of the SSL elements is accelerated.
In addition, in U.S. Pat. No. 6,860,620 titled Light Unit Having Light Emitting Diodes, a light source applicable for car lamp is disclosed. Referring to FIG. 3A, a light source module 300 includes LEDs 320a-320n arranged as a line on a flexible and bendable substrate 310 and covered by an optical lens 330, and further includes a thermal conductive strip-shaped metal plate 340 disposed under the substrate 310, with a thermal conductive tape applied there-between for fixing them together. The assembled structure is shown in FIG. 3B, wherein a metal frame 311 is provided on the substrate 310 and has electric tracks 312, 314, 315 and 317 disposed therein, in which the electric tracks 312 and 315 are used to connect to the anode, and the electric tracks 314 and 317 are used to connect to the cathode. Besides, heat sink tracks 313 and 316 are also included. The light source module provides a bendable light source and also has a heat sink effect. However, the heat sink effect of the light source module 300 is restricted to the heat sink effect achieved at the segmented heat sink tracks on the same side, and a metal frame is also required, which makes a limited contribution to improving the heat sink effect, except for achieving an aesthetic appearance.